Audio amplifier having a low-noise input stage

Abstract

An audio amplifier having a low-noise input stage, being of a type which comprises a gain stage and an output stage cascade connected downstream from said input stage which includes first and second transistors having their respective bases connected to each other via corresponding input resistors, with the base of the first transistor also adapted to constitute a signal input for the amplifier, further comprises an electric connection between the collector of said second transistor and said input resistors to define a diode configuration for that second transistor, thereby the offset effect of the input resistors can be compensated for, and the noise voltage at the output from the amplifier downed.

I claim: 
     
       1. An audio amplifier comprising a low-noise input stage, a gain stage connected to the input stage, and an output stage cascade connected downstream from said gain stage; said input stage comprising first and second transistors having respective base, emitter and collector electrodes, first and second input resistors connected in series between the respective base electrodes of the first and second transistors, means for connecting a signal input for said amplifier to the base electrode of the first transistor, said first transistor being connected in a common emitter configuration with its collector electrode connected to the gain stage and serving as an input to the gain stage, and means for electrically connecting the collector electrode of said second transistor to a node between the series connection of the first and second input resistors whereby said second transistor is in a diode configuration. 
     
     
       2. An amplifier according to claim 1, further comprising a signal input source constituting the signal input of said amplifier, a capacitor, means connecting the base electrode of the first transistor in series with the capacitor and the signal input source to a point of reference potential. 
     
     
       3. An amplifier according to claim 1, wherein the first and second input resistors have the same value whereby the diode configuration of the second transistor functions as a point of reference potential for the signal input to the first transistor base. 
     
     
       4. An amplifier as claimed in claim 3, further comprising third and fourth resistances of the same value respectively connecting the first and second transistor emitters to the point of reference potential.